The overall aim of this project is to assess the neurocognitive mechanisms of judgment and decision-making that may be impaired in recreational MDMA ("Ecstasy") users, and the relationship of these defective mechanisms to the complex strategical and tactical decision-making operations needed to safely drive a motor vehicle. The widespread use of ecstasy by young people causes concern, especially due to its associated risk of traffic accidents. Epidemiological research and case studies have shown that impaired judgment and higher risk taking are the most likely contributors to ecstasy-related traffic accidents. Research also shows that there is a link between recreational ecstasy use, possible serotonin neurotoxicity, decline in decision-making, impulse control, and other mechanisms of executive functions, and a potential impact on driving behavior. These problems seem to remain long after the recreational use of Ecstasy has ceased, suggesting that the neuropharmacological damage may be long lasting or permanent. Although the residual cognitive effects of ecstasy have been studied extensively in drug free ecstasy users, these studies have focused primarily on mechanisms of memory, divided attention, semantic recognition, verbal reasoning and learning. Very little is known about how ecstasy impacts directly the mechanisms of judgment/decision-making, working memory, and impulse control, in abstinent users. Therefore, we will test a series of hypotheses on cognition and driving behavior in ecstasy users. Our overall hypothesis is that recreational use of MDMA, and to a lesser extent other drugs (e.g. cannabis), will produce residual cognitive effects that in turn result in errors in judgment during the driving task. These errors in judgment are directly related to decline in specific executive functions as measured by neuropsychological tests of frontal lobe functions. Elucidation of the residual effects of ecstasy on judgment, decision-making, and impulse control has several important practical consequences, in addition to its obvious value in advancing fundamental knowledge in cognitive neuroscience. On the medical front, it will help determine the conditions under which substance abuse leads to a decline in frontal lobe functions. On the social front, the study helps shed more light on how to identify individuals who may present a risk to others and to themselves on the road.